\"A diamond is forever\" is one of the most successful advertising slogans of al
ID: 514950 • Letter: #
Question
"A diamond is forever" is one of the most successful advertising slogans of all time. Bui is it true? For the reaction shown below, calculate the standard free energy change at 298 K and determine whether or not a diamond is "forever." C(diamond) rightarrow C(graphite Data: Delta H_f degree (diamond) = 1.895 kJ/mol; S degree (diamond) = 2.337 J mol^-1 K^-1; S degree (graphite) = 5.740 J mol^_1K^-1 A) Delta G degree = 2.19 kJ; forever B) G degree = -1.90 kJ; not forever C) Delta G degree = 1.90 kJ; forever D) Delta G degree = -2.90 kJ; not forever E) Delta G degree =Explanation / Answer
since deltaG= deltaH-T*deltaS
for graphite to diamond, deltaH=-1.895 Kj/mole
given deltaH= -1.895 Kj/mole and deltaS= change in entropy = 5.740 - 2.337= 3.403J/mole.K
deltaG= -1.895*1000-298*3.403 = -2909 J/mole= -2.909 Kj/mole since deltaH is -ve it is not for ever. D is correct.
2.
deltaH= -136.3-187.7= 51.4 Kj/mole, deltas= 232.7-109.6= 123.1 J/k.mol
deltaG= -105.6+120.4= 14.8 Kj/mole
since deltaG= deltaH-T*deltas
at equilibrium, deltaG=0 and T= Normal boiling point of =deltaH/deltas= 51.4*1000/123.1= 418 deg.c ( E is correct)